I have been lurking and learning for a while and I think I have a couple questions that can't be answered by doing a search. I have learned so much from just reading what you guys have to say and first I want to thank you for your time and knowledge.

I am just getting into this hobby and my first load will be for a Browning BAR in 7mm Rem Mag. My plan is to start with 162g Hornday SST's because they seem like a good tradeoff between price/performance, and I like the cannelure that some of the other brands around that size/caliber lack. Maybe I'm being overly concerned about that, but it seems like a good idea to keep the bullet where it aught to be on a semi-auto, and it gives me that much more assurance that I have the seating depth right at the seating stage.

My first question is about powder. I have been reading a lot of threads where people are trying to figure out what the best powder is for 7mm Rem Mag. Some of the more popular ones seem to be IMR 4350, RL 22 and H4831SC. The negatives that I have read about them are the RL 22 is temperature sensitive and less consistent as well as being an extruded powder that won't meter all that well (http://forums.handloads.com/forum_posts.asp?TID=9636). IMR 4350 seems to turn in somewhat lower velocities according to the data books and is also temperature sensitive (http://forums.handloads.com/forum_posts.asp?TID=2860).

That left me with H4831SC, but there is something strange about it. In comparing the load data, I see:

Am I reading this right? The min load from Hodgdon is greater than the max from Hornday? Which should I believe? Typo? I guess Hornady could be playing it safe there, or they might be taking better measurements than Hodgdon. The difference could be coming from the primers, could it affect the safe load range by that wide of a margin? It seems that Hornady has done something like this before (http://forums.handloads.com/forum_posts.asp?TID=5449) so maybe I should just use the Hodgdon's data and work up from their 60.0g min load?

A few other options would be Supreme 780, Hybrid 100V or Retumbo. I was a little leary of Supreme 780 because it is so new and I read that they have been trying to produce a reliable Winchester magnum spherical powder for a while, and that prior attempts have had problems. Others have had accuracy problems with Retumbo (http://forums.handloads.com/forum_posts.asp?TID=11679). Very little has been said here about Supreme 780 or Hybrid 100V. I am open to trying them out, but they are unproven. The load weights for Hybrid 100V would let me save a bit on powder costs, but the difference is trivial. On the other hand, I think that Hybrid 100V is double based, which would make it senstive to temperature changes, correct?

A whole other angle came up in a thread started by Stuffit (My condolences, I will miss him as well.) that said you may need to be careful with anything slower than Varget in a Browning BAR for fear of fowling the gas mechanism with unburnt powder. (http://forums.handloads.com/forum_posts.asp?TID=17095)

All of this is theoretical from my point of view so far, so feel free to shoot holes in anything that I've said or thought. I do realize that accuracy is more important than speed, but it seems like with some tuning (powder weight, the BOSS, etc) I might be able to have the best of both worlds. So, I thought I'd start with a powder that can give the higher velocities and go from there.

In short, I'm going for near fastest velocity, best accuracy, temperature insensitivity and best metering all in one powder for that perfect load. Not too much to ask is it? Based on my limited knowledge so far, it seems like the best bet would be Supreme 780 with H4831SC a close second (based on lower velocities). What do you think?

First thing that comes to mind is loading dies. RCBS makes a sizing die specifically for the Browning BAR.

If you have trouble with feeding or extraction consider the RCBS die. I haven't had a single malfunction with my 7MM BAR after I started using the RCBS BAR sizing die. I honestly don't know what the difference is between the die made for the BAR and a standard sizing die, just know that it works.

7MM data varies greatly among the various sources. One of the manuals, sorry I don't recall which one, said the data was reduced for 7MM Mag from previous editions because the loads were hard on barrels. The powders I've used were IMR 4320, IMR 4895, Winchester 760, and both H and IMR 4350. Bullets used were Hornady, one weighed apx 139 and the other about 165. All powders seemed equal as far as accuracy and I didn't have a crony at the time. None of the loads I worked up reached the published max before I started seeing signs of high pressure. The same load showing signs of excessive pressure in my BAR shot perfect with no high pressure signs in a friend's bolt action Remington 700.

Your best bet for conflicting data is to check as many sources as possible. If your BAR is like mine you will get the best accuracy with a load 10% under published max. Other projects kept me from finding the best load for my BAR, I lost my notes but if I remember correctly 10% under max was about as high as I pushed it with excellent shot to shot accuracy. Even with a slightly reduced load the 7MM mag will produce plenty of FPS.

EDIT: After reading Paul's post it got me thinking about primers and crimp. If I remember correctly I only used mag primers with the Winchester 760. My first batch with the 760 produced a considerable muzzle flash. The mag primers reduced the flash significantly. I experimented with various crimps including a heavy crimp with a Lee Factory Crimp die. I don't recall seeing any difference on paper, a trip through a crony may tell a different story. My personal opinion is crimp is over rated as being a significant factor in shot to shot accuracy in rifle ammo. The ideal crimp as far as I'm concerned is one heavy enough to take the rigors of hunting. My BAR is a mid-80's Portuguese model without the BOSS muzzle break.

I put the primers in bold to emphasis the difference in data is due in part to the magnum primer used by Hornady. It seems like they have a propensity for using magnum primers when they aren't needed.

While the pressure may be the same with the two primers and their corresponding data, there is still a matter of gas production that favors the standard primer with a little more powder. That's probably the reason we've gotten by with 68.0 gr of IMR4350 with a 139-140 gr bullet for so long. That's a good load for our M700s, but may not be as good in your BAR.

I think the cannelure is a non-issue with your box magazine. The main reason I can see for it being on the SSTs is to "lock" the core to the jacket. We've never crimped 7mm Mag, we just use a good friction fit.

IMR 4350 should be as "extreme" as any other single based powder, including IMR/H4831.

Metering is much different with the "new" tube size on IMR powders. The old DuPont powders had a much longer/larger tube and they didn't meter worth a hoot. The Canadian powders, whether from DuPont or IMR, are much smaller tubes. Of course, I weight every round of rifle ammunition, so metering is a non-issue for me.

Thanks for the info guys. You definitely gave me some more to think about.

I have already bought an RCBS X-Sizer die for sizing, in the hopes that it will extend case life (http://forums.handloads.com/forum_posts.asp?TID=14791). An open question is how well the output of the X-Sizer will fit my BAR's chamber. I hadn't seen the RCBS BAR die before, but I'll keep it in mind of things don't go well.

I haven't even started to think about crimp, other than the cannelure. I do have a Lee Factory Crimp die, because a good many people seem to be fans of doing crimping separately from seating. I'm guessing that the extra muzzle flash was from unburned powder and that the mag primer gave your a more complete burn?

I was thinking that maybe the primers were making the difference in the two different load ranges given, but it wasn't quite making sense to me. What Paul said about the 68gr of IMR4350 lit my bulb. The mag primers shoot out a bigger flame for a longer period of time, which means that more of the powder will get the initial ignition from the mag primer as opposed to a normal primer. Kind of like lighting all four corners of a piece of paper instead of just one corner. The mag primers should produce more of a pressure spike in the gas, which should mean that you would have to use less of the same powder in the same cartridge with a mag primer. With a normal primer, the powder would ignite in a more progressive manner, with roughly the same amount of gas produced, but over a longer period of time with a more even pressure curve.

That assumes that you have the same powder in the same cartridge. If you change the powder, the burn rate changes and so the pressure curves will be different, as well as the ignition temperatures, etc; so the reaction to the mag/non-mag primers will be different. If a given powder just doesn't ignite well with a normal primer, you might have to use a mag primer just to get it going fast enough (more gas on the fire).

That would mean that if you keep the powder the same but change the cartridge, the volume filled in that cartridge will change, so that more or less of the powder will be directly exposed to the flame of the primer, which will determine how much of the powder is initially ignited. If you only have a half full case, the powder can slop around quite a bit and change the exposed surface area, changing how much powder is initially set off by the primer. Changes in exposed surface area would give wide variances in the pressure curve and affect accuracy, and possibly safety, as the pressure may spike if the powder happens to be dead level in the case when the primer goes off.

That means that you'd want the case to be close to full of powder in order to have a consistent pressure curve, and repeatable shots. I had read that before, but it makes a lot more sense now. That's a whole other angle on this power selection business. I guess if I wanted to be really precise I'd have to try to find the density of the powder and compare it to the case volume. There must be a table that shows case fill % with different powders somewhere, or maybe one of these software packages.

I hadn't looked to see whether or not IMR 4350 was single or double base, but being single base it does seem like it should be fairly insensitive. I'll have to try to find out if Supreme 780 is single or double base.

Thanks again for your help, and if you have any more comments, I'm all ears.

IMR kept the single based powders in the forced breakup of the 1914 time era. Hercules (Alliant) got the double based powders. It has been pretty much the same for almost 100 years now. 700X and 800X are the only two double based powders offered by IMR, to my knowledge.

Most ball/spherical powder is double based and I believe all Winchester powders are ball powders. There may be a single based ball powder, but I don't know of one right off hand.

The old IMR4350 at 68.0 gr was pretty much up into the neck in the 7mm Mag. The newer powder doesn't fill as much due to the smaller tube size. It's sorta like a SC without being advertised as such.

When you have a given powder, there is a known quantity of gas produced per unit of volume or weight. By using a magnum primer, less powder is used and there is less gas produced, even though the pressure may be the same. As the volume increases (while the bullet travels down the barrel) more gas will fill the volume better. That also keeps the pressure at a higher level for a longer period of time.

That's a good history lesson Paul, thank you. I haven't found anything printed to say one way or the other on Supreme 780 being single or double base, but that's enough for me to drop it for now.

What you are saying about gas produced per unit powder, magnum primers and pressures fits as well, I think.

You've mentioned that IMR 4350 load for 7mm before. I wonder if you have tried H4831SC as a comparison? I've seen some other people who like that one as well. I guess having it narrowed down to just two powders I'm to the point that I could just buy two cans and have some fun .

If you dont have a good reason for using a heavy
162 gr bullet for 7mm, I would suggest you drop back
to 135 gr ballpark. This past year I began to shoot
120 gr 7mm rem mag and really liked them.

I am not shooting anything bigger than hogs and
deer so I have concluded for me that 120 is all I
need. I use sierra and nosler bullets.
Also, I must confess, the recoil is much less
on the lighter bullets.

Powder scarceness is a problem right now. I might have to settle for what they have. If they do have anything on the "prefered" list, more is cheaper too.

The 162 grain might be ham handing it. This is one of my bigger guns, so the bigger bullet for bigger game. The 140 grain range seems more popular for 7mm, for the faster muzzle velocities and flatter trajectory. For deer, a smaller bullet seems like it would do just as well.

I'm hoping that the gas operated semi-auto and the boss take some of the recoil out of the gun. They claim that the boss will take off about 30% and the gas operated action will take off about 15%.

Now I am probably going to get some disagreements on this but a load I like is one that is mentioned in the Nolser book (the fifth I think it was anyway) Lee also lists similar data on a 150 grain bullet. Nosler Partition is one I like, but there are others. The powder is IMR -4064, a powder that can be used in several caliber loadings. If you can find it message me. I liked it because the lose of FPS was well made up in recoil, and the ability to stay on target for fast follow up.

Use a Nosler reloading manual to get % of volume for a particular powder, it will give you many options, stick with something in the high 80 to 90+ range so you'll have no issues with powder not covering the primer. Auto's whether service or otherwise need a bit more power to be reliable shot after shot. Newer powders burn cleaner than the older ones which is a plus for your gas system.

Guys this is kind of an old thread but I would like
to update on what I have found to be my new favorite
bullet for big deer and hog hunting. Believe it or
not for the entire deer season this year I went
even lighter with the Barnes 110gr Solid Copper.
Yea I know it first seems like blasphemy but with
those bullets retaining the same weight as a
bullet 30 or 40 grains heavier you get the same
terminal effect AND an incredible laser beam trajectory.

All this with the added benefit of recoil that makes the
rifle feel more like a 25-06 then a magnum caliber.
I'm telling ya I shot 165 and 175 for years and
I have finally seen the light. I would have to
be shooting at buffalo, moose or bears for me to
use a heavier bullet nowadays.

That some good advice about that bar sizing die . It would be that or a small base sizer die for sure .dont take a chanch on a jam up

Best I can tell comparing sized brass with the BAR sizing die and a standard die. The BAR die gives the shoulder a bit more of a nudge. The BAR's shoulder is rounded and the standard die the shoulder is sharp.

Next time I'm at my loading bench I'll mike the belt, possibly the BAR die sizes down the belt a bit more.

I'd sure like to keep this thread alive. Possibly somebody might come along that knows the difference. All I know the BAR sizing die worked for me and I can't recall a single hick-up since I began using it.

You guys posted a lot of good tidbits in this thread, some of which I have come to on my own, and it makes me think I might have actually done some consistent experimentation to reach perhaps valid conclusions. I test my loads off of bags, not a leadsled, so there's plenty of room for shooting error on my part which could bury any validity to my data. But maybe this is actually working! The BAR's somewhat spongy trigger doesn't help with accuracy. That's for another thread though!

I have a BAR in .270 Win, and I experimented with a few powders...H4350, RL22, and finally W760, all with 130gr bullets. I have found W760 to be an excellent match for this gun and cartridge; the best I have tried. It is the fastest of the powders I tried, and it occurred to me that perhaps it performs better in the BAR because the whole burn is complete by the time the auto mechanism is driven. 760 meters so consistenly from a standard RCBS powder drop, its amazing. All drops within .05 - .1 grains, most dead on! Chrono - SD is between 18fps - 35fps, average 22.

When I buy 760, people at the store often seem surprised I use it for the .270...don't know why. I noticed on Win's site they recommend Supreme 780 for teh .270, so that may be even better.

AzRedneck mentioned best accuracy with his BAR happens with reduced loads, and I found the same, but not reduced a full 10%. Max for this cart/bullet combo is 53gr - 56gr depending on the manual and I settled on 52gr.

Here's a very accurate formula:
Hdy 130gr SP, OAL: 3.280", Rem LR primer, 52gr W760
Max for this bullet is 55 or 56gr of W760
This results in a MV of 2840fps.

Hornady 130gr SP are as accurate as any other projectile I've found and are the least expensive. SSTs exhibit same accuracy but better terminal performance. I shoot mostly at paper. 4 shot groups at 100 yrds range from 3 sharing a hole with a flier .7" away, to 1.3" x .75". I think most of the variation is me, as stated above.

As Preventec47 described, I have also been using lighter bullets lately - 110gr Sierra SP. Seated to same as SP 130. Reduced from max, at 56.5gr 760, 4 shot groups are commonly 1 MOA on a calm day. MV is about 3130fps. I could slow it down a little for even less recoil, and I don't think it will affect the accuracy negatively.

A couple months ago at the range the guy next to me was shooting a 270 BAR. He was shooting factory fodder. If I recall correctly he was shooting Winchester "Supreme" ammo but I don't recall the bullet weight. Naturally we compared rifles, my 7MM mag and traded shots. I know much can be attributed to the shooter, scope, ammo and other variables. He had a real nice Loopy and I have a cheapie scope. His beautiful leather sling is probably worth more than my scope. When we compared bench rested 200 yard shot groups I was really embarrassed. His 270 BAR was incredibly more accurate than mine. After being hammered with a my 7MM mag his 270 was really pleasant to shoot.

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